In photography or cinematography, the sharpness of a picture depends on a variety of factors such as steadiness of the camera support, exposure time, and depth of field. Steadiness is poor when the camera is held by hand and can be improved through the use of a tripod, for example. The time of exposure of a photosensitive element depends on shutter speed but, under proper lighting conditions, can also be controlled by the flashing of a strobe light. Depth of field is a function of focal length, diaphragm aperture and object distance; under otherwise equal conditions, blurring is greatest with large focal lengths (e.g. with the use of telephoto lenses).